From: Andrii Nakryiko <andriin@fb.com>
To: <bpf@vger.kernel.org>, <netdev@vger.kernel.org>, <ast@fb.com>,
<daniel@iogearbox.net>
Cc: <andrii.nakryiko@gmail.com>, <kernel-team@fb.com>,
Andrii Nakryiko <andriin@fb.com>
Subject: [PATCH bpf-next 1/2] libbpf: support flexible arrays in CO-RE
Date: Sat, 14 Dec 2019 23:08:43 -0800 [thread overview]
Message-ID: <20191215070844.1014385-2-andriin@fb.com> (raw)
In-Reply-To: <20191215070844.1014385-1-andriin@fb.com>
Some data stuctures in kernel are defined with either zero-sized array or
flexible (dimensionless) array at the end of a struct. Actual data of such
array follows in memory immediately after the end of that struct, forming its
variable-sized "body" of elements. Support such access pattern in CO-RE
relocation handling.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
tools/lib/bpf/libbpf.c | 34 +++++++++++++++++++++++++++++-----
1 file changed, 29 insertions(+), 5 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 27d5f7ecba32..51e7a25c6c88 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2537,6 +2537,21 @@ static bool str_is_empty(const char *s)
return !s || !s[0];
}
+static bool is_flex_arr(const struct btf *btf,
+ const struct bpf_core_accessor *acc,
+ const struct btf_array *arr)
+{
+ const struct btf_type *t;
+
+ /* not a flexible array, if not inside a struct or has non-zero size */
+ if (!acc->name || arr->nelems > 0)
+ return false;
+
+ /* has to be the last member of enclosing struct */
+ t = btf__type_by_id(btf, acc->type_id);
+ return acc->idx == btf_vlen(t) - 1;
+}
+
/*
* Turn bpf_field_reloc into a low- and high-level spec representation,
* validating correctness along the way, as well as calculating resulting
@@ -2574,6 +2589,7 @@ static int bpf_core_spec_parse(const struct btf *btf,
struct bpf_core_spec *spec)
{
int access_idx, parsed_len, i;
+ struct bpf_core_accessor *acc;
const struct btf_type *t;
const char *name;
__u32 id;
@@ -2621,6 +2637,7 @@ static int bpf_core_spec_parse(const struct btf *btf,
return -EINVAL;
access_idx = spec->raw_spec[i];
+ acc = &spec->spec[spec->len];
if (btf_is_composite(t)) {
const struct btf_member *m;
@@ -2638,18 +2655,23 @@ static int bpf_core_spec_parse(const struct btf *btf,
if (str_is_empty(name))
return -EINVAL;
- spec->spec[spec->len].type_id = id;
- spec->spec[spec->len].idx = access_idx;
- spec->spec[spec->len].name = name;
+ acc->type_id = id;
+ acc->idx = access_idx;
+ acc->name = name;
spec->len++;
}
id = m->type;
} else if (btf_is_array(t)) {
const struct btf_array *a = btf_array(t);
+ bool flex;
t = skip_mods_and_typedefs(btf, a->type, &id);
- if (!t || access_idx >= a->nelems)
+ if (!t)
+ return -EINVAL;
+
+ flex = is_flex_arr(btf, acc - 1, a);
+ if (!flex && access_idx >= a->nelems)
return -EINVAL;
spec->spec[spec->len].type_id = id;
@@ -2954,12 +2976,14 @@ static int bpf_core_spec_match(struct bpf_core_spec *local_spec,
*/
if (i > 0) {
const struct btf_array *a;
+ bool flex;
if (!btf_is_array(targ_type))
return 0;
a = btf_array(targ_type);
- if (local_acc->idx >= a->nelems)
+ flex = is_flex_arr(targ_btf, targ_acc - 1, a);
+ if (!flex && local_acc->idx >= a->nelems)
return 0;
if (!skip_mods_and_typedefs(targ_btf, a->type,
&targ_id))
--
2.17.1
next prev parent reply other threads:[~2019-12-15 7:09 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-15 7:08 [PATCH bpf-next 0/2] CO-RE relocation support for flexible arrays Andrii Nakryiko
2019-12-15 7:08 ` Andrii Nakryiko [this message]
2019-12-15 7:08 ` [PATCH bpf-next 2/2] selftests/bpf: add flexible array relocation tests Andrii Nakryiko
2019-12-16 0:56 ` [PATCH bpf-next 0/2] CO-RE relocation support for flexible arrays Alexei Starovoitov
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